cleaning the initializeExitSide of the Cell subclasses.
add beamPath chapter beginning
startin back
Merge pull request #2 from bencoman/master

Chapters 1, 3 & 4.
mering
Merge branch 'master' of github.com:SquareBracketAssociates/PharoLaserGameTutorial
addin textual representation to debug
Merge SquareBrackets into BenComan fork.